Process for transporting particles in a porous medium

ABSTRACT

The invention relates to an improved method for injecting and transporting small particles in a natural porous medium. The method is characterized in that, in a first step, the porous medium is conditioned by means of an aqueous solution containing a hydrocarbonaceous compound, polymers or surface-active agents, in a second step, a plug of suspended particles is injected in the aqueous medium containing at least one hydrocarbonaceous compound, polymer or surface-active agent and, in a third step, the plug of particles is pushed by an appropriate aqueous medium. The method is particularly useful for implantation of bacteria in a porous medium.

FIELD OF THE INVENTION

The subject of the present invention is an improved process forinjecting and transporting particles, especially microorganisms, in aporous natural medium.

DESCRIPTION OF THE PRIOR ART

The so-called primary and secondary techniques for recovering oil, whenused efficiently, lead to the extraction of not more than 35% to 40% ofthe crude oil contained in a reservoir. The so-called tertiary improvedrecovery techniques consist in extracting all or part of this residualoil especially by flushing the zone with water with the aim, either ofmodifying the properties of the oil in situ, or of modifying theproperties of the water used for flushing, by increasing its viscosityvia the addition of water-soluble organic polymers, or by reducing thephenomena of repulsion between the water and the oil via the addition ofsurfactants.

Another known technique, which is different in concept and application,is the closing-off of the high-permeability zones of the reservoir whichare very damaging to the oil production, using high-viscosity polymersobtained, where appropriate, by cross-linkages.

The polymer compounds or surfactants used in these various types ofprocess may be either synthetic (produced chemically) or natural (forexample produced microbiologically using microorganisms, especiallybacteria, which are capable of converting, via metabolism, suitablecarbon substrates such as sugars or hydrocarbons).

These processes and compounds are for example described in U.S. Pat. No.3,650,326 which relates to an assisted recovery process in which anaqueous flushing medium is used which comprises a viscosity-promotingagent produced by bacterial culture, the mixture of viscosity-promotingagent, bacteria and cultural medium being introduced into the flushingmedium.

U.S. Pat. No. 3,598,181 describes a similar process, specifying theimportant role played by an anionic surfactant in the formation of theviscosity-promoting agent.

U.S. Pat. No. 3,763,934 describes a process for closing up permeableformations using various synthetic polymers such as polyacrylamides,cellulose derivatives and water-soluble gums.

European Patent Application No. 073 612 illustrates the use of mixturesof the biopolymer xanthan- and polyglycol-type surfactants forcontrolling the mobility of the solution.

Furthermore, consideration has already been given to the production insitu, inside the formation, of the biosurfactant or biopolymericproducts required for the specific application considered, by injectingthe microorganisms, the appropriate substrate and their nutritiveelements into this formation. Such processes are described in particularin U.S. Pat. Nos. 3,340,930 and 4,522,261.

The success of the production in situ naturally depends on the selectionof the appropriate strains capable of developing inside the formationenvironment, but also on the ability to enable the microorganism toreach its destination, that is to say the formation to be treated,without being blocked, along the long distance to be covered, in alow-permeability zone or without the microorganism meeting agrowth-stimulating substrate en route which brings about itsmultiplication and/or the production of compounds creating a plug whichcan for example bring about the closing-up of the injection wells.

The success of such a process therefore depends substantially on thequality of the cell migration within the porous media which exhibitlarge variations in porosity and permeability. This major difficultycertainly explains why this type of process has rarely been used by theoil industry and is used essentially as an ultimate course of actionwhen the well is intended to be closed down eventually.

SUMMARY OF THE INVENTION

The object of the invention is to overcome this disadvantage byproposing means which promote the transit of particulate suspensions,especially bacterial suspensions, through porous natural media.

These means for transporting particulate suspensions, especiallybacterial suspensions, in porous media, have been studied not only withrespect to processes for the improved recovery of oil, but also to anyprocess in which there is a need to transport small, solid particles, inporous media and especially the problem of soil and ground waterrehabilitation for which it may be essential to implant, and thereforeto transport, bacterial suspensions which enable a purification ordepollution activity to be obtained in situ microbiologically. The caseof the protection of natural storage sites for which it might beadvantageous to implant biological systems which improve the confinementof stored materials, may also be mentioned.

The subject of the invention is a process for injecting and propagatingsmall, solid particles in a porous natural medium characterised in that,in a first stage, the said medium is conditioned by flushing with abalanced aqueous solution containing at least one hydrocarbon compoundchosen from water-soluble or water-dispersible polymers and anionicsurfactants and then, in a second stage, a plug of solid particles,suspended in a balanced aqueous medium and containing, in addition, atleast one hydrocarbon compound chosen from water-soluble orwater-dispersible polymers, and the anionic surfactants are injectedinto the said medium and, in a third stage, the said plug of particlesis thrust by an appropriate aqueous medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a laboratory device for carrying out the experimentsdescribed in the specification.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment of the process of the invention, at least onehydrocarbon compound chosen from water-soluble or water-dispersiblepolymers and anionic surfactants is added to the thrust medium.

It can be stated that the hydrocarbon compounds used in each of thevariousstages may be identical or different. Their nature is independentof the solid particle which is injected and propagated.

The process of the invention applies to the injection and thepropagation, inside porous media, of suspensions of small particles,called micron particles, that is to say whose mean diameter is not morethan about 10×10⁻⁶ m. The choice of the particles to be injected willdepend on the specific application envisaged. These particles can be ofnatural and/or mineral origin, for example bentonites, clays or latex.In a preferred application of the process, they may consist of bacterialcells capable of producing in situ compounds which enable the porousmedium to be treated in an satisfactory manner where they are implanted.

In a preferred application of the process of the invention, viable,non-pathogenic bacterial cells, which are used under non-proliferativeconditions, are used as particles.

These bacterial cells can be for example:

aerobic Gram-negative rods or cocci, Pseudomonadaceae family;(Pseudomonas-Xanthomonas genera); Halobacteriaceae family;(Halobacterium-Halococcus genera);

facultative, anaerobic Gram-negative rods; Enterobacteriaceae family;Vibrionaceae family;

anaerobic Gram-negative bacteria; Desulfovibrio genus;

chemolithotrophic Gram-negative bacteria; Nitrobacteriaceae family;Thiobacillus/Sulfolobus genera;

methane-producing bacteria; Methanobacteriaceae family;

facultative, anaerobic Gram-positive cocci, or aerobes; Micrococcaceaefamily; Streptococcaceae family (Leuconostoc genus);

endospore-forming rods and cocci; Bacillaceae family(Bacillus-Clostridium genera);

-non-Sporeforming Gram-positive bacteria in the form of rods;Lactobacillaceae family;

Gram-positive bacteria belonging to the Actinomycete and related groups;Actinomycetaceae family; Nocardiaceae family; Micromonosporaceae family;Streptomycetaceae family.

The aqueous solutions or media used in the process should be balanced.Balanced is understood, in the present application, to mean an aqueoussolution or medium which is compatible with the water in the porousmediumto be treated, which can be achieved for example by adding theprincipal salts of the porous medium to be treated, to the said mediumor solution. The presence of salts in the suspension is important forspecific propagation of the particles injected into the porous medium.Indeed, it avoids the mobilisation of clays or any other colloidalparticle present in the porous medium and, furthermore, it preserves theintegrity of the particles transported, especially if they are bacterialcells, by limitingthe phenomena of osmotic swelling. It is important forthe fluid injected to be compatible with the chemical nature of theporous medium treated. The ionic composition of the fluid can be forexample a reconstituted edgewater containing MgCl₂, 6H₂ O; CaCl₂, 2H₂ O;K₂ SO₄ ; Na₂ SO₄ ; FeSO₄, 7H₂ O; NaCl. It can be very simplified in somecases and call into play only one salt (NaCl) or a mixture of two saltsNaCl and CaCl₂, whose proportion canbe varied according to the nature ofthe porous medium to be treated.

The hydrocarbon compound used in one of the stages can be an anionicsurface-active agent which can be used alone or mixed with other anionicor nonionic surface-active agents. The total concentration ofsurfactants will generally be between 10⁻⁵ mole.1⁻¹ and 10⁻¹ mole.1⁻¹and preferably between 10⁻⁵ and 10⁻³ mole.1⁻¹. The surface-active agentconcentration in the aqueous medium will depend on the choice of thesurfactant and on the geochemical nature of the formation to be treated: pH and salinity of the formation in particular. For example asurfactant concentration and the total amountto be injected will dependon the salinity of the water in the formation that is to say its alkalimetal cation content and its alkaline-earth metal cation content. Thehigher the concentration of alkaline-earth metalcations, the higher willbe the amount of surfactant to be injected, and therefore itsconcentration in the aqueous injection medium. On the other hand, if thesalinity is due to a high concentration of alkali metal cation, theamount of surfactant required for the process will be relatively smallerthan in the presence of alkaline-earth metal cations.

The following may be used for example as anionic surface-active agent:

fatty acid soaps such as the sodium or potassium salts of saturated orunsaturated C₁₀ -C₂₄ fatty acids or aminocarboxylic acid derivativessuch as sodium N-lauryl sarconisate,

sulphates and sulphated products such as sodium lauryl sulphate typealkalimetal alkyl sulphates; polyoxyethylenated fatty alcohol sulphates,polyoxyethylenated alkylphenol sulphates, polyoxyethylenatedarylalkylphenol sulphates,

phosphoric esters of oxyethylenated derivatives such aspolyoxyethylenated fatty alcohol phosphates, polyoxyethylenatedalkylphenol phosphates, polyoxyethylenated arylalkylphenol phosphates,

alkali metal sulphonates such as alkyl sulphonates for example sodiumdialkyl sulphosuccinate type C₄ -C₃₀ acid alkyl sulphoesters,alkylbenzenesulphonates such as sodium nonylbenzenesulphonate and sodiumdodecylbenzenesulphonate and lignosulphonates.

Naturally, when bacterial cells are injected, it will be ensured that asurfactant is chosen which is non-toxic to the said cells and which iscompatible with the porous medium to be treated.

The hydrocarbon compound used in one of the stages can be a highmolecular weight viscosity-promoting water-soluble or water-dispersiblepolymer. Thepresence of this polymer makes it possible in particular tostabilize the suspension of particles. High-molecular weightviscosity-promoting polymeris understood to mean a polymer with amolecular weight above 500,000 daltons and preferably between 1 and 10million daltons. This polymer should not be susceptible to the action ofbacteria which may be present.

The following may be mentioned as examples of polymers which may be usedinthe process of the invention:

synthetic polymers such as partially hydrolysed polyacrylamides,acrylamide-acrylic acid copolymers, acrylamide-acrylate copolymers,salified polyacrylates, salified polymethacrylates, partially hydrolysedpolyacrylonitriles, polystyrenesulphonates, sulphonated styrene-maleicanhydride copolymers and the like,

biopolymers such as xanthan, scleroglucan, dextran, polyhydroxybutyrates(PHB), mannans, pullulan, curdlan and the like,

cellulose derivatives: carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, carboxymethyl hydroxyethyl cellulose and the like,

natural polymers: gum arabic, alginates.

The polymer content of the aqueous injection medium will be in generalbetween 10 and 5,000 ppm and preferably between 50 and 450 ppm.

The preferred polymer of the process of the invention will be apartially hydrolysed polyacrylamide (PAA). The degree of hydrolysis willgenerally be between 10% and 70% and preferably between 15% and 35%.

In a variant of the process of the invention, the aqueous medium forinjecting the particles in the second stage will contain, in addition tothe salts, a mixture of water-soluble or water-dispersible polymers andananionic surfactant. The polymer and surfactant contents of the aqueousinjection medium will be similar to those described above for processesusing the surfactant or polymer alone.

It may also be advantageous to use a polymersurfactant mixture duringthe first conditioning stage.

The amount of particulate suspensions, especially of bacteria, to beinjected should be commensurate with the pore volume to be treated. Inthecase of the treatment of an oil deposit, this will involve highpermeability zones which in general represent not more than a few % ofthetotal volume of the porous medium. The amount of suspensions to beinjectedwill take into account this pore volume to be treated as wellas, to a certain extent, the pore volume of the transit zone, that is tosay the distance separating the injection zone and the zone to betreated. The amount of particles to be suspended is generally between10⁵ and 10¹⁰ particles per cm³.

During implementation of the process, an aqueous fluid containing thehydrocarbon compounds without the particles is injected followed by anaqueous injection medium containing all the elements; the total amountof surfactant and/or polymer should be sufficient to ensure adequateconditioning of the zones through which the particulate suspension mustpass. In general, the total volume of the solution of aqueous fluid usedfor the first two stages will scarcely exceed 30% of the total volume ofthe porous medium and will often be less than 20% of this volume, andthe amount of hydrocarbon compound will be optimized as a function ofthe specific surface area of the porous medium.

The volume of suspension injected in the second stage, that is to saythe plug, will represent in general between 10% and 50% of the volumeinjectedin the first stage and will in general be between 2% and 10% ofthe total pore volume of the porous medium.

The process of the invention will be best understood on reading theexamples below given merely by way of illustration.

Examples 1 to 4 below relate to bacteria belonging to theStreptococcaceae family and more particularly to the Leuconostoc genus.The bacterium is Leuconostoc mesenteroides.

EXAMPLES 1 to 4

The experiments were carried out in a laboratory device in which acolumn with a length of 18 cm and an inner diameter of 2.54 cm is filledwith Entraygues sand and possesses a pore volume of 45 cm³ (Vp).

This very siliceous sand (98% silica) contains very little clay and doesnot require prior treatment so as to avoid disturbances in themeasurements carried out on the reconstituted porous media.

The particles consist of Leuconostoc mesenteroides bacteria cultured ona glucose-based medium and consisting of the usual nutritive elements.At the end of the exponential phase, the culture is centrifuged at 9,500revolutions per minute for 15 minutes and washed in a 0.1 N solution ofNaCl. Three centrifugation-resuspension cycles make it possible toremove the components of the culture medium which could perturbsubsequent measurements.

The polymer used is 25%-hydrolysed "BASF SEPAFLOOD" polyacrylamidediluted to 250 ppm in aqueous solution (PAAH).

The anionic surfactant used is sodium dodecyl sulphate (SDS) at aconcentration of 10⁻³ M/l.

The laboratory device used is described below with reference to FIG. 1given herewith.

This device comprises:

reservoirs (1), (2) and (3) containing fluids which are injectedsuccessively in a column (4) filled with the appropriate porous medium(5),

a set of capillary tubes (7) in which the fluids, carried by a syringepump(6), circulate,

a six-way and a two-position injection valve (8) which makes it possibletoinject a known volume of the suspension (5) contained in the injectionloop(9),

the column of porous medium (5) , packed or unpacked, has dispersingends (10) and (10') which are suitable for distributing the fluid at theinlet and at the outlet of the column, and allowing circulation both ofthe solutes and of the injected particles,

two on-line detectors: a UV spectrophotometer (11) adjusted at 280 nmwhichprovides a measurement of the optical density which is correlatedwith the particle concentration, and a conduct meter (12) which enablesvariations in salinity in the effluent to be recorded,

a fraction collector (13) which enables subsequent additionalmeasurements to be carried out on the effluent,

a pressure sensor (14) at the termini of the column enabling the headloss to be evaluated.

In Example 1, the Entraygues sand constituting the porous medium was, ina first stage, flushed with a 0.1 M/l saline solution of NaCl until aneffluent with a steady composition was obtained.

In a second stage, a volume of particles containing 5-7.10⁸ particlesper cm³ of suspension is injected, via the injection loop, into a salinesolution identical to that of the first stage, pulse corresponding to 2%of the pore volume of the column (45 cm³) . The column is maintainedunder a continuous flow of the solution at a steady flow rate of 0.2 cm³min⁻¹ which permits push-type displacement of the volume of particles.

In Example 2, the saline solutions are replaced for all the stages by a0.1M/l solution of NaCl supplemented with 250 ppm of PAAH.

In Example 3, the saline solution is replaced for both the stages by a0.1 M/l solution of NaCl supplemented with 10⁻³ M.1⁻¹ SDS.

In Example 4, Example 1 is repeated replacing the saline solution with a0.1 M/l saline solution of NaCl supplemented with 250 ppm of PAAH and10⁻³ M.1⁻¹ SDS.

The operating conditions for each of these examples and the resultsobtained, expressed as % restitution of the injected particles: numberof particles recovered/number of particles, by measurement of theoptical density after calibration, are summarised in Table 1 below.

It can be observed that, in the absence of the anionic hydrocarboncompounds of the process of the invention, closing-up of the column andalmost total retention of the bacteria in the porous medium is obtained,which corresponds to an increase in head loss in the column (Example 1)whereas this increase in the column is practically nonexistent inExamples2 to 4, which corresponds to an excellent percentagerestitution.

                  TABLE 1                                                         ______________________________________                                                         Composition  Injected                                                         of the aqueous                                                                             volume  %                                             Particle con-                                                                            phase (salts (as % of                                                                              Resti-                                  No.   centration/ml                                                                            and additives)                                                                             the V.sub.p)                                                                          tution                                  ______________________________________                                        1     5-7.10.sup.8                                                                             NaCl: 10.sup.-1 N                                                                          2       0.05                                    2     5-7.10.sup.8                                                                             NaCl: 10.sup.-1 N                                                                          2       25                                                       PAA 250 ppm                                                  3     5-7.10.sup.8                                                                             NaCl: 10.sup.-1 N                                                                          2       42                                                       SDS 10.sup.-3 M.1.sup.-1                                     4     5-7.10.sup.8                                                                             NaCl: 10.sup.-1 N                                                                          2       48                                                       PAA 250 ppm and                                                               SDS 10.sup.-3 M.1.sup.-1                                     ______________________________________                                    

EXAMPLES 5 to 22

The same experiment was carried out, using various hydrocarboncompounds, on several types of solid particles (Lueconostocmesenteroides bacteria, Bacillus subtilis bacteria, bentonite).

The precise operating conditions for the various stages and the resultsobtained for each of the examples are shown in Table 2 below.

The general conditions for these experiments and the abbreviations usedin Table 2 are as follows:

1) CONDITIONING STAGE

The volume is expressed as Vp, that is to say the total pore volume ofthe medium.

The conditioning medium still contains 0.1 N NaCl, which is not statedin the table, supplemented, where appropriate, with:

Sodium dodecyl sulphate, 10⁻³ mole/l:abbreviated S

30%-hydrolysed polyacrylamide, 250 ppm: abbreviated P

2) PLUG INJECTION STAGE

The plug volume is equal to 0.02 Vp.

The injection medium contains, as particles, Leuconostoc mesenteroidesbacteria, that is 10¹⁰ bacteria per ml in Examples 5 to 16, except forExample 13 where 10⁹ bacteria/ml were injected:abbreviated L.

2.5 10⁹ Bacillus subthis bacteria per ml in Examples 17 and18:abbreviated B.

100 ppm of bentonite in Examples 19 to 21: abbreviated b.

The injection medium still contains 0.1 N NaCl (not mentioned) and,where appropriate, the products termed S and P above in the sameamounts, or 250ppm of sodium lignosulphonates : abbreviated l.

3) Thrust medium

The aqueous solution will still contain 0.1 N NaCl and, whereappropriate, the abovementioned products P and l in the same amounts.

Restitution of the particles injected as a volume (plug) is evaluated atthe outlet of the porous medium by the amount of particles recovered foravolume of thrust medium equal to 1 Vp, expressed in % relative to theamount injected.

                  TABLE 2                                                         ______________________________________                                                                 Particle                                                                              Thrust                                       Ex.   vol     Conditioning                                                                             injection                                                                             water   Resti-                               No.   (Vp)    composition                                                                              composition                                                                           composition                                                                           tution %                             ______________________________________                                         5    0.1     S          L       --      3.9                                   6    2.0     S          L       --      27.0                                  7    --      --         L + P   --      0.1                                   8    --      --         L + P + S                                                                             --      0.6                                   9    0.5     S + P      L + P + S                                                                             --      77.0                                 10    sat     P          L + P   P       70.5                                 11    0.5     P          L + P   P       58.0                                 12    0.2     P          L + P   P       53.0                                 13    0.2     P          L + P   P       46.0                                 14    0.2     P          L + S   1       56.0                                 15    0.2     P          L + 1   --      33.0                                 16    0.2     P          L + P + S                                                                             --      24.7                                 17    --      --         B + S   P       15.5                                 18    0.2     P          B + S   P       26.5                                 19    --      --         b       --      0.1                                  20    0.2     P          b       --      3.0                                  21    0.2     P          b + p   P       33.0                                 ______________________________________                                    

"sat" means medium saturated with the aqueous conditioning medium

Comparison of the results obtained in these different experimentsreveals arole played by each of the different stages of the process andthe effect of the simultaneous use of a polymer and a surfactant.

Experiments 5 to 8 demonstrate the low efficiency of the process usingonlyone hydrocarbon compound in only one of the stages. Only aconditioning of 2 times the pore volume, which is incompatible with asatisfactory implementation of the process (experiment 6), permitssubstantial transportation of particles.

In contrast, as soon as the three stages are implemented successively(experiments 11 to 14), transportation of not less than 50% of theparticles is achieved after a thrust which is one-fold the pore volume.

The advantage of the thrust stage is clearly demonstrated by experiments19to 21. Starting with a restitution which is practically non-existentwhen bentonite is injected without additives, restitution to a porevolume of 33% is achieved by implementing the complete process.

It is possible to use Bacillus (experiments 17 and 18) which areparticles two times larger than Leuconostoc. The restitution, which issubstantial, is less satisfactory however: 26.5% compared with the 50%on average obtained above.

Sodium lignosulphonate appears to be an excellent product provided thatit can be used without problems of toxicity (experiments 14 and 15).

We claim:
 1. Process for injecting and propagating small, solidbacterial or mineral micron particles in a porous natural medium bypromoting their transit through the porous natural medium, wherein in afirst stage, the said medium is conditioned by flushing with a balancedaqueous solution containing at least one hydrocarbon compound selectedfrom the group consisting of water-soluble polymers, water-dispersiblepolymers and anionic surfactants and then, in a second stage, a plug ofsolid particles, suspended in a balanced aqueous medium and containing,in addition, at least one hydrocarbon compound selected from the groupconsisting of water-soluble polymers, water-dispersible polymers and ananionic surfactant is injected into the said medium, wherein the anionicsurfactant in the aqueous medium is present in an amount of between 10⁻⁵and 10⁻¹ M/l, and, in a third stage, the said plug of particles isthrust by an appropriate aqueous medium.
 2. Process according to claim1, wherein the aqueous thrust medium used in the third stage contains atleast one hydrocarbon compound selected from the group consisting ofwater-soluble polymers, water-dispersible polymers and anionicsurfactants.
 3. Process according to any one of claims 1 and 2, whereinthe polymer in the aqueous medium has a molecular mass above 500,000daltons.
 4. Process according to claim 3, wherein the polymer content ofthe aqueous medium is between 10 and 5,000 ppm.
 5. Process according toclaim 4, wherein the polymer is a natural or synthetic water-dispersiblepolymer.
 6. Process according to claim 5, wherein the polymer is apartially hydrolyzed polyacrylamide.
 7. Process according to claim 4,wherein the polymer is a partially hydrolyzed polyacrylamide.
 8. Processaccording to claim 3, wherein the polymer is a partially hydrolyzedpolyacrylamide.
 9. Process according to any one of claims 1 and 2,wherein in the first conditioning stage, the porous medium is flushedwith a volume of aqueous solution representing less than 30% of thetotal pore volume to be treated.
 10. Process according to claim 9,wherein the amount of aqueous medium injected in the second stagerepresents 2% to 10% of the total pore volume to be treated.
 11. Processaccording to claim 10, wherein the bacterial content of the aqueousmedium is between 10⁵ and 10¹⁰ bacteria per ml.
 12. Process according toany one of claims 1 and 2, wherein the polymer in the aqueous medium hasa molecular mass between 1.10⁶ and 10.10⁶ daltons.
 13. Process accordingto claim 1, wherein the aqueous medium used in the second stagesimultaneously contains an anionic surface-active agent and a polymer ofmolecular mass above 500,000 daltons.
 14. Process according to claim 13,wherein the polymer is present in an amount between 10 and 5,000 ppm.